Plastic materials have various advantages, such as lightness, design flexibility and moldability, despite lower thermal resistance and flame resistance than metals or ceramics, and thus are widely used as materials in a variety of products from daily supplies to industrial fields including automobiles and electric/electronic products.
There are various types of plastic materials from commodity plastics to engineering plastics that are widely used in various fields requiring various functions and performances.
Among these plastic materials, polyphenylene ether has excellent electrical and mechanical properties and high thermal deflection temperature to be used as engineering plastics in various fields.
Polyphenylene ether was developed by General Electric in the U.S.A., and is used in the form of blends with high impact resistance polystyrenes as useful industrial materials, based on excellent thermal resistance thereof. Recently, polyphenylene ether is used in alloy form such as polypropylene/polyphenylene ether obtained by adding a polyamide/polyphenylene ether resin and a compatibilizer as a third component, followed by reaction extrusion for compatibilization of non-compatible blends through a chemical process.
Particularly, polyamide/polyphenylene ether can effectively remedy shortcomings of each resin component, thereby exhibiting good balance between thermal resistance, impact resistance and chemical resistance, and is thus employed in exterior components of automobiles, such as a hubcap, a junction box, and the like, and engine compartment components of automobiles.
Recently, there is a need for a plastic material for exterior components which allows on-line electrostatic plating such that electrostatic plating can be simultaneously performed on the plastic material and other metal components. In order to meet such a need, a conductive polyamide/polyphenylene ether resin developed by General Electric can be applied to automobile fender components (EP 685527 B1)
Such a conductive polyamide/polyphenylene ether resin can allow plastic exterior components formed of the resin to be subjected to electrostatic painting simultaneously with other metal material components to eliminate a need for an additional painting process, thereby reducing production costs.
In order to impart electrical conductivity to the polyamide/polyphenylene ether alloy, it is suggested that conductive fillers such as carbon fibers and carbon black be added thereto (JP H04-300956 A). However, carbon fibers can cause deterioration in formability and typical carbon black must be added in a large amount in order to achieve electrical conductivity for application to electrostatic plating, thereby causing deterioration in impact resistance and formability.
In order to overcome these problems of impact resistance and formability, nanoscale carbon fibers (carbon fibrils) or conductive carbon black having adjusted size are used (JP 2756548 B2). However, this method has a problem of deterioration in compatibility of the polyamide/polyphenylene ether resin.
In order to prepare a polyamide/polyphenylene ether resin having excellent physical properties without deterioration in compatibility, it is important to secure efficient compatibilization between a polyphenylene ether, a polyamide, and a compatibilizer upon extrusion.
In a typical method, in order to secure efficient compatibilization, first, the polyamide and the polyphenylene ether are compatibilized, followed by adding conductive carbon black thereto (EP 685527 B1).
However, this method is performed using special extrusion facilities including a plurality of side feeders and requires a particular sequence of adding the polyamide/polyphenylene ether alloys, the compatibilizer and other additives. Thus, this method is uneconomical due to expensive facility investment and has low productivity due to restriction on the sequence of adding raw materials.
Therefore, in order to solve the above problems, the inventors carried out studies to develop a conductive polyamide/polyphenylene ether resin composition, which can maintain excellent inherent properties of the polyamide and the polyphenylene ether, is applicable to on-line electrostatic plating, and has improved properties and economic feasibility.